While I agree with this idealistically and wish that all the code I've come across adhered to published interfaces, unfortunately that hasn't been the case.
Published interfaces may also not be possible in certain code bases or frameworks -- think of a Chef recipe for instance where most (ruby) code is being written to directly interact with the system rather than provide a service to other parts of the system. Dynamically generating variable names and key/value pairs in Chef recipes is a common pattern I've seen which makes grepping and isolating issues difficult if not impossible.
Published interfaces may also not be possible in certain code bases or frameworks -- think of a Chef recipe for instance where most (ruby) code is being written to directly interact with the system rather than provide a service to other parts of the system. Dynamically generating variable names and key/value pairs in Chef recipes is a common pattern I've seen which makes grepping and isolating issues difficult if not impossible.